Temperature compensated reference voltage circuitry employing current limiters and reference voltage diodes



Dec. 22, 1970 c. K. WALTERS 3,549,938

TEMPERATURE COMPENSATED REFERENCE VOLTAGE CIRCUITRY EMPLOYING CURRENT .LIMI'I'ERS AND REFERENCE VOLTAGE DIODES v 2 Sheets-Sheet 1 Filed Jan. 2. 1 968 CURRENT LIMITER CURRENT LIMITER CURRENT LIMITER l6d l2 l6e 2 I ZENER DIODE (Low Voltage) F/GZ F/G3 (GVOLTS V: 9O VOLTS+ V2) TOTAL INPUT VOLTAGE VOLTAGE ACROSS v T1 \sE CURRENT LIMITER T 2; 2 4 2 6 I V 42 '02 Milliomperes 2 (below crossover polrl) -ssc +25%: +50% Y 0.6 Mlliiumperes 28 3Q 32 I (above o ossover polnr) I 0.8 Mllllomperes so (parallel combination of two current limiters) +l50C -55C CURRENT F/G 4 INVENTOR.

C ecf/ K. Walters Dec. 22, 1970 TEMPERATURE coin C K. WALTERS ENSATED REFERENCE VOLTAGE Filed Jan. 2, 1968 2 Sheets-Sheet 2 TOTAL INPUT VOLTAGE 6 Volfs+ V2 90 Volts V:

ZENE R VOLTAGE 6 VOLTS 9O VOLTS For MCL-' TOTAL INPUT VOLTAGE 6 Volts +Vz -90 Volts Vz --ZENER VOLTAGE -6 VOLTS- 9OVOLTS For MCL Vz I I 55C +25C 5O I T ST$I$2529$3- T I I 50C 52 54 I I 0.4 Milllomporus A: Crossover Point 121 5 CURRENT REFERENCE VOLTAGE 0,4 Milliomperes A1 i I I I l Crossover Point I TYPICAL VOLTAGE VS CURRENT OF AVALANCHE AND ZENER BREAKDOWN Avalanche Breakdown I-- Zener Breakdown I 1" I I Q 3 -55c I+25c- 4 +|5oc (In) In Milfiampercs H6 8 INVENTORL Ceci/ K. l lblrers BY IN/Mafia, die/Me, {27W United States Patent O 3,549,988 TEMPERATURE COMPENSATED REFERENCE VOLTAGE CIRCUITRY EMPLOYING CUR- RENT LIMITERS AND REFERENCE VOLT- AGE DIODES Cecil Kent Walters, Scottsdale, Ariz., assignor to M- torola, Inc., Franklin Park, Ill., a corporation of Illinois Filed Jan. 2, 1968, Ser. No. 695,183

Int. Cl. Gf 3/02 US. Cl. 3239 4 Claims ABSTRACT OF THE DISCLOSURE Reference voltage circuitry in which one or more current limiters, such as field effect diodes, are connected to a zero temperature coefiicient (0 TC) reference or Zener diode and are selected to drive the 0 TC reference diode in a manner to provide a constant output voltage over wide ranges of temperature and input voltage.

BACKGROUND OF THE INVENTION This invention relates generally to reference voltage circuitry and more particularly to a circuit capable of producing a reference voltage which does not vary with changes in ambient temperature.

It is well known to connect a 0 TC reference diode across a source of constant reverse current and bias the diode in its breakdown or Zener mode of operation to provide a constant reference voltage output for variations of temperature. Previously, however, a constant current voltage source was required for the 0 TC reference voltage diode if the diode was to produce a constant reference voltage with changes in temperature, i.e., have a zero temperature coeflicient of voltage with variations in ambient temperature. The requirement for a bulky, external constant current source is disadvantageous since such source cannot be readily incorporated into the package for the reference voltage circuit. Also, constant current sources are generally affected by temperature themselves and therefore affect the 0 TC reference diode in a detrimental fashion. The present invention eliminates this problem and introduces a temperature compensated current source for operation of the well known 0 TC reference diode. Testing of a current source with a 0 TC reference Zener diode of known temperature characteristics allows for compensation techniques in the design of a temperature compensated voltage circuit which otherwise would be impossible. These techniques will be described below.

SUMMARY OF THE INVENTION An object of this invention is to provide a new and improved zero temperature coefficient (0 TC) reference voltage circuit.

Another object of this invention is to provide a reference voltage circuit which does not require an external constant current input source and from which a constant output voltage may be derived over a wide range of ambient temperatures and input voltages.

Briefly described, this invention is directed to a reference voltage circuit in which one or more current limiters are connected in parallel between a source of input voltage and a reference voltage output terminal. A 0 TC reference Zener diode is connected between the output terminal and a point of reference potential and is biased in a Zener mode. The temperature coefficients for the current limiter (or current limiters) and the reference diode are selected so that the output voltage across the diode remains constant over a wide range of ambient temperature.

Patented Dec. 22, 1970 ICC FIG. 1 illustrates in block diagram one embodiment of the invention in which a single current limiter is employed in combination with a 0 TC reference voltage Zener diode;

FIG. 2 illustrates another embodiment of the invention in which multiple current limiters are employed in parallel combination with a 0 TC reference voltage Zener diode;

FIG. 3 illustrates a further circuit embodiment of the invention in which multiple current limiters are connected to a reverse biased Zener diode in a low voltage reference circuit;

FIG. 4 is a graphic illustration of how multiple current limiters are matched to provide a constant output current to a 0 TC reference Zener diode. FIG. 4 also illustrates how multiple current limiters are combined with a 0 TC reference diode in accordance with this invention to provide a constant output reference voltage over a given temperature range;

FIG. 5 is a graphic illustration of how a single current limiter with a positive temperature coefficient of current (FIG. 1) is matched with a 0 TC reference diode with a negative temperature coeflicient of voltage (or vice versa, not shown) to provide a constant output reference voltage. The circuit combination of the 0 TC reference diode and current limiter exhibit a zero temperature coefficient (0 TC) of voltage.

FIG. 6 is a graphic illustration of how a current limiter with a zero temperature coefficient of current is combined with a 0 TC reference diode;

FIG. 7 is a graphic illustration of how a reverse biased Zener diode of high dynamic impedance and current limiter in FIG. 3 are temperature matched; and

FIG. 8 is a graphic illustration which distinguishes avalanche breakdown with Zener breakdown of reference diodes operating at different temperatures.

Referring to the drawings in more detail, there is shown in FIG. 1 a reference voltage circuit having an input terminal 10 which is connectable to an input voltage source (not shown) and a current limiter 16 connected between terminal 10 and an output terminal 12 at which a constant voltage may be derived. Current limiter 16 may for example, be a field effect diode with the source and gate electrodes thereof connected together. A 0 TC reference Zener diode 18 is connected between the output terminal 12 and a point of reference potential 19 and provides a reverse breakdown voltage of zero temperature coefiicient.

The circuit in FIG. 2 differs from the circuit in FIG. 1 in that multiple current limiters 16a and 16b are connected in parallel between input terminal 10 and output terminal 12. The operation of the reference voltage circuits in FIGS. 1 and 2 will be more fully understood by referring to the graphs in FIGS. 4 and 5.

The circuit embodiment in FIG. 3 includes a reverse biased diode 21 which is connected between current limiters 16 and ground, and diode 21 breaks over at a low voltage with negative temperature coefficient. The circuit in FIG. 3 will be described further below with reference to the graph in FIG. 7.

In accordance with one embodiment of the invention illustrated in FIG. 4, it is desired to limit the current into the reference diode 18 to a value which is above the crossover current level for a particular family of current limiters. The cross-over current level of these current limiters and referred to hereinafter as the cross-over point is defined as that point at which the pinch-off current for the current limiter (or limiters) does not vary with temperature over a range of temperatures varying for example, from 55 C. to C. At levels of pinch-off current I below the cross-over point, a current limiter has a positive temperature coeflicient (TC) of current and at levels of pinch-off current I above the cross-over point a current limiter has a negative temperature coefiicient of current. Therefore, if it is desired to maintain a constant pinch-oif current I at levels of current above the crossover point, then, in accordance with the present invention, multiple current limiters are matched so that the negative temperature coefiicient of current of a current limiter having a value of I above the cross-over point will counteract or offset the positive temperature coefiicient of current for a current limiter having a value of I below the cross-over point.

As illustrated in FIG. 2, a first current limiter 16a having a positive temperature coeflicient of current as indicated by curves 22, 24 and 26 over the temperature range from -55 C. to +150 C. is connected in parallel with a current limiter 16b having a negative temperature coefficient of current. The current limiter 16b exhibits characteristic curves 28, 30' and 32 over the temperature range of between -5S C. and +l50 C., and the overall decrease in pinch-off current I for current limiter 16b over the above temperature range is equal in absolute magnitude to the overall increase in pinch-off current 1,, for current limiter 16a and represented by curves 22, 24 and 26. Therefore, the resultant total pinch-off current I total for the parallel combination of current limiters 16a and 1617 will remain constant over the above temperature range. This value of I total is represented by the characteristic curve 50 in FIG. 4. The mean value of pinch-off current 1 i.e., at 25 C., for the current limiter 16a is approximately 0.2 milliampere, a value of I below the current cross-over point. The current limiter 16b has a mean value of I equal to approximately 0.6 milliampere, a value of I above the current cross-over point which is approximately 0.4 milliampere for the graphic illustration in FIG. 4.

The first embodiment of the invention described above and directed solely to the combination of current limiters to provide a desired pinch-off current I which is invariant over a wide temperature range has been referred to as a zero temperature coeflicient current limiter circuit and abbreviated as TCCL circuit.

In a second embodiment of the present invention which is also illustrated in FIG. 4, multiple current limiters, such as current limiters 16a and 16b in FIG. 2, are combined with a 0 TC reference voltage Zener diode 18 to provide a reference voltage at terminal -12 which remains constant over a temperature range from 55 C. to +150 C. The 0 TC reference diode 18 (FIG. 2) is selected to have a zero temperature coefficient of voltage at a value of current I which corresponds to that value of current 1,, of the multiple current limiters. Therefore, the Zener diode 18 is biased into operation at a fixed point 47, the voltage at which does not change over the above temperature range. The Zener diode 18 may be said to have a zero temperature coefficient (0 TC) of voltage at point 47 which is matched to a value of I at which the combination of current limiters 16a and 16b has a 0 TC. As the temperature at the Zener diode changes from 5 5 C. to +150 C., the Zener characteristic will Change as indicated by curves 42, 44 and 46 but all of these characteristic Zener curves pass through the operating point 47 at which the Zener voltage remains constant. For variations in input voltage ranging from 6 volts to 90 volts plus the voltage V across the Zener diode 18, the output terminal 12 in FIG. 2 will always be clamped at the Zener voltage V This voltage is controlled by the design of the well known 0 TC reference diode. The above-described embodiment of the invention in which the multiple current limiters are matched to a 0 TC Zener diode has been identified as the current limiter-zero temperature coefiicient reference voltage circuit and abbreviated CL 0 TC circuit.

In a third embodiment of the invention which is illustrated in FIG. 5, a single current limiter 16 of positive temperature coefficient is matched to a 0 TC reference diode 18 of negative temperature coefficient (or vice versa, not shown) in a zero temperature coefficient (0 TC) reference voltage circuit which is shown in FIG. 1. The 0 TC diode 18 and the current limiter 16 are matched so that the output voltage across the Zener diode 18 will be constant over the temperature range between 55 C. and +150 C. This embodiment of the invention will be referred to as the current limiter compensated zero temperature coefficient reference voltage circuit and abbreviated as CLC 0 TC circuit. In FIG. 5, a current limiter 16 having a positive temperature coefficient of current as illustrated by curves 50, 52, and 54 is matched to a 0 TC reference diode 18 having a negative temperature coefficient of voltage at the operating point as illustrated by curves 56, 58 and 60. The temperature dependent current of the current limiter 16 and temperature dependent voltage of the 0 TC reference diode 18 respectively, are matched so that a constant reference voltage is maintained over the above temperature range corresponding to the operation points of intersection 62, 64 and 66. The output reference voltage V will remain constant for variations in input voltage ranging from the pinch-off voltage of the current limiter, e.g., 6 volts plus the Zener voltage (V of diode 18 to approximately volts plus V In a fourth embodiment of the present invention which is illustrated in FIG. 6, a single current limiter 16 (FIG. 1) having a pinch-off current I at the current cross-over point is connected in a reference voltage circuit with a 0 TC reference diode 18 having a zero temperature coefficient of voltage at the current cross-over point. Thus, for a level of current indicated by curve 68 and typically in the order of 0.4 milliampere, the Zener voltage V, of the diode 18 will always be constant. The characteristic curves 65, 67 and 69 in FIG. 6 all pass through the operating point 76, and therefore a constant voltage V for a current level of I at the crossover point is maintained. However, it should be understood that the present invention is not limited to a particular value of cross-over current such as 0.4 milliampere, since this value may vary typically between 0.1 milliampere and 1 milliampere. The embodiment of the invention illustrated in FIGS. 1 and 6 is referred to as current limiter cross-over zero temperature coefficient reference voltage circuit and abbreviated CLX 0 TC.

A fifth embodiment of the present invention is illustrated in FIGS. 3 and 7 wherein current limiters 16c, 16d and 162 are connected to a low voltage reverse biased diode 21 operating in the Zener breakdown region. The diode 21 is selected to provide an output reference voltage at output terminal 12, with a zero temperature coefiicient of voltage when operating in combination with current limiters 16c, 16d and 16s. This Zener voltage is typically in the order of one to six volts (at a reference current of one milliamp) for silicon diodes. In this voltage region, Zener breakdown predominates over avalanche breakdown. Zener breakdown will exhibit a negative temperature coefficient of voltage as well as a comparatively high dynamic impedance when compared with the sharp avalanche breakdown (FIG. 8). The dynamic impedance may be measured by superimposing a ten percent modulation of test current to measure the impedance in the vicinity of any desired test current. With the proper selection of current limiters connected in parallel and exhibiting a positive temperature coefficient of current, a Zener breakdown device with negative temperature coefiicient of voltage may be compensated to yield a constant voltage with variation in temperature according to the principles illustrated in FIG. 3 and FIG. 7.

In the region where Zener breakdown diminishes and avalanche breakdown becomes predominate (typically five volts at one milliamp), a reference diode approximating a zero temperature coefficient voltage device will be obtained. This type of device may be operated in conjunction with single or multiple current limiters as set forth in FIG. 1 or 2 and the second or fourth embodiment of this invention.

For application with Zener diodes having a negative temperature coefiicient, each current limiter should have a pinch-off current I below the cross-over point and a positive temperature coefficient of current over the temperature range from 55 C. to +150 C. The current limiter characteristic curves 71, 73 and 75 indicate a large increase in current with temperature where temperature T T T The negative temperature coefficient characteristic of the Zener diode curves 74, 76, and 78 do not intersect as do the TC reference diode curves in FIGS. 4, 5 and 6. The Zener avalanche transition at approximately five volts as previously described may exhibit a characteristic of intersection as does the 0 TC reference diode in FIGS. 4, 5 and 6. The Zener diode curve 74, 76 and 78 intersect the current limiter curves 70, 73 and 75 at points 84, 82 and 80, respectively, so that the reference voltage circuit always provides a constant output voltage. The embodiment of the invention illustrated in FIGS. 3 and 7 is referred to as current limiter-Zener zero temperature coefficient reference voltage circuit and abbreviated as CLZ 0 TC circuit.

-1 claim:

1. A reference voltage circuit including in combination:

a first current limiter connected between a voltage input terminal and a voltage output terminal, said first current limiter having a positive temperature coefficient of current over a predetermined range and at current below the zero temperature coefiicient current level,

a second current limiter connected in parallel with said first current limiter and having a negative temperature coefficient of current for levels of current above said Zero temperature coefiicient current level whereby the temperature coeflicient of said first current limiter is offset and compensated by the temperature coefiicient of said second current limiter and the total output current from the parallel connected first and second current limiters remains constant over said predetermined temperature range, and

a reference voltage diode connected between said output terminal and a point of reference potential, said diode having a zero temperature coefficient of voltage for a selected level of total current output from said first and second current limiters, whereby the voltage across said reference diode remains constant for variations in ambient temperature and input voltage.

2. A reference voltage circuit including, in combination:

a current limiter connected between a voltage input terminal and a voltage output terminal and having 50 a nonlinear current-voltage characteristic with a substantially constant value of pinch off current for a selected range of voltage above a given value of pinch off voltage, said current limiter further having a preselected temperature coeflicient of current, and

a reference voltage diode connected between said current limiter and a point of reference potential and having a preselected temperature coefficient of voltage which produces an increase or decrease respecticely in current flow therethrough by an amount equal to the increase or decrease respectively, in current flow through said current limiter due to temperature changes so that the point of intersection of the current-voltage characteristic of said current limiter and current-voltage characteristic of said reference diode remains at a constant output voltage, thereby maintaining the output voltage across said diode constant over a predetermined temperature range.

3. A reference voltage circuit including, in combination:

a current limiter connected between a circuit input terminal and a circuit output terminal and having a nonlinear current voltage characteristic with a substantially constant value of pinch off current corresponding to a range of applied voltage above a given pinch off voltage, said current limiter further having a zero temperature coefficient of current at a given limiting current, and

a reference voltage diode connected betwen said current limiter and a point of reference potential and having a zero temperature coefficient of voltage at an operating current corresponding to the limiting current through said current limiter.

4. A reference voltage circuit including in combination:

current limiters connected in parallel between a voltage input terminal and a voltage output terminal and having a preselected temperature coefiicient of current, and

a Zener biased diode connected between said current limiters and a point of reference potential and having a preselected temperature coefficient of voltage which produces a change in current flow therethrough by an amount equal to the change in current flow through said current limiters due to temperature changes thereat so that the point of intersection of the current-voltage characteristics of said current limiters and the current-voltage characteristic of said Zener diode remains at a constant output voltage, thereby maintaining the output voltage across said Zener diode constant over a predetermined temperature range.

References Cited UNITED STATES PATENTS 3,025,455 3/1962 Ionsson 323--68 3,293,540 12/1966 Silard et al. 32368 3,300,710 1/1967 Knauss 32317 3,303,413 2/1967 Warner, Jr., et al. 323-4 3,471,712 10/1969 Tomozawa et al. 307-205 OTHER REFERENCES Field-Effect Transistors: Physics, Technology and applications, edited by Wallmark and Johnson, 1966 by Prentice-Hall, Inc. (Pub), pages 359-263 relied upon.

I D MILLER, Primary Examiner G. GOLDBERG, Assistant Examiner U.S. Cl. X.R. 

